1. Field of the Invention
The present invention relates to a hard disk drive (HDD), and more particularly, to a method and apparatus for controlling the rotation of a motor in an HDD.
2. Description of Related Art
Hard disk drives (HDDs) of various types are used in various mobile devices such as car navigation systems, car personal computers (PCs), portable media players (PMPs), portable media centers (PMCs), and cell phones.
The HDD has a spindle motor which rotates a disk at a constant angular velocity. Thus, a head of the HDD is raised above the disk by a dynamic pressure due to the rotation of the disk in order to perform magnetic recording/reading on/from the surface of the rotating disk. Recently, a fluid dynamic bearing (FDB) has been used in the spindle motor to reduce noise and vibrations, and increase the performance and reliability of the HDD.
The viscosity of the FDB rapidly increases when the temperature decreases, thereby significantly decreasing a bearing capacity due to viscous friction. Thus, below a specific low temperature, the spindle motor cannot spin-up a disk up to a target rotation speed set when the HDD was designed.
In particular, a mobile device using such HDD may be used at temperatures between −30° C. and 80° C. In general, since a viscous friction of a fluid bearing rapidly increases at a very low temperature of −30° C., a torque constant of the spindle motor must be set to a low value in order to rotate the spindle motor up to the rated rotation speed. As a result, the HDD requires a high driving current, which increases power consumption.
Thus, according to a conventional method and apparatus for controlling the rotation of a motor in an HDD, since the rotation of the motor cannot be increased at a very low temperature, a normal operation of the HDD cannot be performed, thereby decreasing reliability of a device using the HDD. In addition, for a normal operation of the device, an excessive driving current is required.